Backing Yardage Calculator

How the backing math works

Your backing has to be bigger than the quilt top so there's something to hold onto while you baste and quilt — usually 4 inches past every edge for a longarm. Once the backing is wider than a single width of fabric (about 42″), you have to seam two or more lengths together.

A worked example: backing that same 60″ × 72″ throw

With a 4″ overhang on every side and 42″ of usable width — the calculator's defaults:

Both layouts need two widths, but turning the seam sideways saves 24 inches of fabric — most of a half yard, for free. The calculator always works out both and shows you the cheaper one, which is the single most useful thing it does.

Vertical vs. horizontal seams

There are usually two ways to seam a back and they rarely use the same amount of fabric, because you are choosing which dimension of the quilt gets covered by the 42″ direction of the yardage. Neither is stronger; a seam pressed open lies flat either way. Longarm quilters often prefer the seam running parallel to the roller, so ask yours if you are sending it out. Wide-back fabric (108″) skips the seam entirely — set the usable width to 108 to compare the cost.

Common mistakes

Using 4″ overhang for a domestic machine. Four inches a side is a longarm requirement, because the quilt is loaded onto rollers. Quilting it yourself on a domestic machine, 2″ is usually plenty and saves fabric — see the overhang guide. Leaving the selvages in the seam. Selvage is denser than the rest of the fabric and will pucker; trim it off both edges before seaming. Pressing the backing seam to one side. Press it open so no ridge sits under the quilting. Forgetting the seam allowance itself — two 42″ widths joined give about 83″, not 84″.

Common questions

Can I use a bed sheet as backing?

You can, but the thread count is usually much tighter than quilting cotton, which makes hand quilting hard and can fight a longarm needle. If you do, wash it first.

How do I piece a back from leftover blocks?

That is a pieced back, and the yardage works differently because you are combining scraps rather than buying width. Pieced quilt backs walks through it.

Why is my backing 3⅞ yards when the quilt is only 2 yards long?

Because it takes two widths of fabric to cover the quilt's width, and you buy each width at full length. Two 68″ lengths is 136″ of yardage even though the quilt is 80″.